While doing some memory scanning of military frequencies tonight, I
was reminded how much I'd like to be able to optimize the squelch
setting for each channel individually.

Some HF radios offer "syllabic squelch" which is not a response to ANY signal,
but looks only for specific characteristics of voice (syllables)

Harris 505 has this, (but no scanning) as do the Scientic Radio System units.

Such radios do not respond to noise, so you find that you don't have to adjust
squelch for day/night differences